This invention pertains to the field of genetic vaccines. Specifically, the invention provides multi-component genetic vaccines that contain components that are optimized for a particular vaccination goal. In a particular aspect this invention provides methods for improving the efficacy of genetic vaccines by providing materials that facilitate targeting of a genetic vaccine to a particular tissue or cell type of interest.
This invention also pertains to the field of modulation of immune responses such as those induced by genetic vaccines and also pertains to the field of methods for developing immunogens that can induce efficient immune responses against a broad range of antigens.
Thus, the present invention also relates generally to novel proteins, and fragments thereof, as well as nucleic acids which encode these proteins, and methods of making and using these proteins in diagnostic, prophylactic and therapeutic applications. In a particular exemplification, the present invention relates to proteins from the Plasmodium falciparum erythrocyte membrane protein 1 (xe2x80x9cPfEMP1xe2x80x9d) gene family and fragments thereof which are derived from malaria parasitized erythrocytes. In particular, these proteins are derived from the erythrocyte membrane protein of Plasmodium falciparum parasitized erythrocytes, also termed xe2x80x9cPFEMP1xe2x80x9d. The present invention also provides nucleic acids encoding these proteins, which proteins and nucleic acids are associated with the pathology of malaria infections, and which may be used as vaccines or other prophylactic treatments for the prevention of malaria infections, and/or in diagnosing and treating the symptoms of patients who suffer from malaria and associated diseases.
This invention also relates to the field of protein engineering. Specifically, this invention relates to a directed evolution method for preparing a polynucleotide encoding a polypeptide. More specifically, this invention relates to a method of using mutagenesis to generate a novel polynucleotide encoding a novel polypeptide, which novel polypeptide is itself an improved biological molecule and/or contributes to the generation of another improved biological molecule. More specifically still, this invention relates to a method of performing both non-stochastic polynucleotide chimerization and non-stochastic site-directed point mutagenesis.
Thus, in one aspect, this invention relates to a method of generating a progeny set of chimeric polynucleotide(s) by means that are synthetic and non-stochastic, and where the design of the progeny polynucleotide(s) is derived by analysis of a parental set of polynucleotides and/or of the polypeptides correspondingly encoded by the parental polynucleotides. In another aspect this invention relates to a method of performing site-directed mutagenesis using means that are exhaustive, systematic, and non-stochastic.
Furthermore this invention relates to a step of selecting from among a generated set of progeny molecules a subset comprised of particularly desirable species, including by a process termed end-selection, which subset may then be screened further. This invention also relates to the step of screening a set of polynucleotides for the production of a polypeptide and/or of another expressed biological molecule having a useful property.
Novel biological molecules whose manufacture is taught by this invention include genes, gene pathways, and any molecules whose expression is affected thereby, including directly encoded polypetides and/or any molecules affected by such polypeptides. Said novel biological molecules include those that contain a carbohydrate, a lipid, a nucleic acid, and/or a protein component, and specific but non-limiting examples of these include antibiotics, antibodies, enzymes, and steroidal and non-steroidal hormones.
In a particular non-limiting aspect, the present invention relates to enzymes, particularly to thermostable enzymes, and to their generation by directed evolution. More particularly, the present invention relates to thermostable enzymes which are stable at high temperatures and which have improved activity at lower temperatures.
Genetic immunization represents a novel mechanism of inducing protective humoral and cellular immunity. Vectors for genetic vaccinations generally consist of DNA that includes a promoter/enhancer sequence, the gene of interest and a polyadenylation/transcriptional terminator sequence. After intramuscular or intradermal injection, the gene of interest is expressed, followed by recognition of the resulting protein by the cells of the immune system. Genetic immunizations provide means to induce protective immunity even in situations when the pathogens are poorly characterized or cannot be isolated or cultured in laboratory environment.
The efficacy of genetic vaccination is often limited by inefficient uptake of genetic vaccine vectors into cells. Generally, less than 1% of the muscle or skin cells at the sites of injections express the gene of interest. Even a small improvement in the efficiency of genetic vaccine vectors to enter the cells can result in a dramatic increase in the level of immune response induced by genetic vaccination. A vector typically has to cross many barriers which can result in only a very minor fraction of the DNA ever being expressed.
Limitations to immunogenicity include: loss of vector due to nucleases present in blood and tissues; inefficient entry of DNA into a cell; inefficient entry of DNA into the nucleus of the cell and preference of DNA for other compartments; lack of DNA stability in the nucleus (factor limiting nuclear stability may differ from those affecting other cellular and extracellular compartments), and, for vectors that integrate into the chromosome, the efficiency of integration and the site of integration. Moreover, for many applications of genetic vaccines, it is preferable for the genetic vaccine to enter a particular target tissue or cell.
Thus, a need exists for genetic vaccines that can be targeted to specific cell and tissue types of interest, and which exhibit an increased ability to enter the target cells. The present invention fulfills these and other needs.
Elicitation of a desired in vivo response by a genetic vaccine generally requires multiple cellular processes in a complex sequence. Several potential pathways exist along which a genetic vaccine can exert its effect on the mammalian immune system. In one pathway, the genetic vaccine vector enters cells that are the predominant cell type in the tissue that receives vaccine (e.g., muscle or epithelial cells). These cells express and release the antigen encoded by the vector. The vaccine vector can be engineered to have the antigen released as an intact protein from living transfected cells (i.e., via a secretion process) or directed to a membrane-bound form on the surface of these cells. Antigen can also be released from an intracellular compartment of such cells if those cells die.
The antigen derived from vaccine vector internalization and antigen expression within the predominant cell type in the tissue ends up within APC. which then process the antigen internally to prime MHC Class I and or Class II, essential steps in activation of CD4+ T-helper cells and development of potent specific immune responses,
Extracellular antigen derived from any of these situations interacts with antigen presenting cells (APC) either by binding to the cell surface (specifically via IgM or via other non-immunoglobulin receptors) and subsequent endocytosis of outer membrane, or by fluid phase micropinocytosis wherein the APC internalizes extracellular fluid and its contents into an endocytic compartment. Interaction with APC may occur before or after partial proteolytic cleavage in the extracellular environment. In any case, the antigen derived from vaccine vector internalization and antigen expression within the predominant cell type in the tissue ends up within APC. The APC then process the antigen internally to prime MHC Class I and or Class II, essential steps in activation of CD4+ T-helper cells (TH1 and/or TH2) and development of potent specific immune responses.
In a parallel pathway, the genetic vaccine plasmid enters APC (or the predominant cell type in the tissue) and, instead of antigen derived from plasmid expression being directed to extracellular export, antigen is proteolytically cleaved in the cell cytoplasm (in a proteasome dependent or independent process). Often, intracellular processing in such cells occurs via proteasomal degradation into peptides that are recognized by the TAP-1 and TAP-2 proteins and transported into the lumen of the rough endoplasmic reticulum (RER).
The peptide fragments transported into the RER complex with MHC Class I. Such antigen fragments are then expressed on the cell surface in association with Class I. CD8+ cytotoxic T lymphocytes (CTL) bearing specific T cell receptor then recognize the complex and can, in the presence of appropriate additional signals, differentiate into functional CTLs.
In addition, poorly characterized pathways, which are generally not dominant, exist in APC for trafficking of cytoplasmically generated peptides into endosomal compartments where they can end up complexed with MHC Class II, and thereby act to present antigen peptides to CD4+TH1 and TH2 cells. Because activation, proliferation, differentiation and immunoglobulin isotype switching by B lymphocytes requires help of CD4+T cells, antigen presentation in the context of MHC Class II molecules is crucial for induction of antigen-specific antibodies. By virtue of this pathway, a genetic vaccine vector can lead to CD4+T cell stimulation in addition to the dominant CD8+CTL activation process described above. This alternative pathway is, however, of little consequence in muscle cells where levels of MHC Class II expression are very low or zero.
Genetic vaccination can also elicit cytokine release from cells that bind to or take up DNA. So-called immunostimulatory or adjuvant properties of DNA are derived from its interaction with cells that internalize DNA. Cytokines can be released from cells that bind and/or internalize DNA in the absence of gene transcription. Separately, interaction of antigen with APC followed by presentation and specific recognition also stimulates release of cytokines that have positive feedback effects on these cells and other immune cells. Chief among these effects are the direction of CD4+TH cells to differentiate/ proliferate preferentially to TH1 or TH2 phenotypes. Furthermore, cytokines released at the site of DNA vaccination, regardless of the mechanism of their release, contribute to recruitment of other immune cells from the immediate local area and more distant sites such as draining lymph nodes. In recognition of the importance of cytokines in elicitation of a potent immune response, some investigators have included the genes for one or more cytokines in the DNA vaccine plasmid along with the target antigen for immunization. In this case cytokines are derived not only from processes intrinsic to the interaction of DNA with cells, or specific cell responses to the antigen, but via synthesis directed by the vaccine plasmid.
Immune cells are recruited to the site of immunization from distant sites or the bloodstream. Specific and non-specific immune responses are then greatly amplified. Immune cells, including APC, bearing antigen fragments complexed to MHC molecules or even expressing antigen from uptake of plasmid, also move from the immunization site to other sites (blood, hence to all tissues; lymph nodes; spleen) where additional immune recruitment and qualitative and quantitative development of the immune response ensue.
While these pathways often compete, previously available genetic vaccines have incorporated all components for influencing each of the pathways into a single polynucleotide molecule. Because separate cell types are involved in the complex interactions required for a potent immune response to a genetic vaccine vector, mutually. incompatible consequences can arise from administration of a genetic vaccine that is incorporated in a single vector molecule. Current genetic vaccine vectors employ simple methods for expression of the desired antigen with few if any design elements that control the precise intracellular fate of the antigen or the immunological consequences of antigen expression. Thus, although genetic vaccines show great promise for vaccine research and development, the need for major improvements and several severe limitations of these technologies are apparent.
Largely due to the lack of suitable laboratory models, none of the existing genetic vaccine vectors have been optimized for human tissues. The existing genetic vaccine vectors typically provide low and short-lasting expression of the antigen of interest, and even large quantities of DNA do not always result in sufficiently high expression levels to induce protective immune responses. Because the mechanisms of the vector entry into the cells and transfer into the nucleus are poorly understood, virtually no attempts have been made to improve these key properties. Similarly, little is known about the mechanisms that regulate the maintenance of vector functions, including gene expression. Furthermore, although there is increasing amount of data indicating that specific sequences alter the immunostimulatory properties of the DNA, rational engineering is a very laborious and time-consuming approach when using this information to generate vector backbones with improved immunomodulatory properties.
Moreover, presently available genetic vaccine vectors do not provide sufficient stability, inducibility or levels of expression in vivo to satisfy the desire for vaccines which can deliver booster immunization without additional vaccine administration. Booster immunizations are typically required 3-4 weeks after the primary injection with existing genetic vaccines.
Therefore a need exists for improved genetic vaccine vectors and formulations, and methods for development of such vectors. The present invention fulfills these and other needs.
The interactions between pathogens and hosts are results of millions of years of evolution, during which the mammalian immune system has evolved sophisticated means to counterattack pathogen invasions. However, bacterial and viral pathogens have simultaneously gained a number of mechanisms to improve their virulence and survival in hosts, providing a major challenge for vaccine research and development despite the powers of modem techniques of molecular and cellular biology. Similar to the evolution of pathogen antigens, several cancer antigens are likely to have gained means to downregulate their immunogenicity as a mechanism to escape the host immune system.
Efficient vaccine development is also hampered by the antigenic heterogeneity of different strains of pathogens, driven in part by evolutionary forces as means for the pathogens to escape immune defenses. Pathogens also reduce their immunogenicity by selecting antigens that are difficult to express, process and/or transport in host cells, thereby reducing the availability of immunogenic peptides to the molecules initiating and modulating immune responses. The mechanisms associated with these challenges are complex, multivariate and rather poorly characterized. Accordingly, a need exists for vaccines that can induce a protective immune response against bacterial and viral pathogens. The present invention fulfills this and other needs.
Antigen processing and presentation is only one factor which determines the effectiveness of vaccination, whether performed with genetic vaccines or more classical methods. Other molecules involved in determining vaccine effectiveness include cytokines (interleukins, interferons, chemokines, hematopoietic growth factors, tumor necrosis factors and transforming growth factors), which are small molecular weight proteins that regulate maturation, activation, proliferation and differentiation of the cells of the immune system.
Characteristic features of cytokines are pleiotropy and redundancy; that is, one cytokine often has several functions and a given function is often mediated by more than one cytokine. In addition, several cytokines have additive or synergistic effects with other cytokines, and a number of cytokines also share receptor components.
Due to the complexity of the cytokine networks, studies on the physiological significance of a given cytokine have been difficult, although recent studies using cytokine gene-deficient mice have significantly improved our understanding on the functions of cytokines in vivo. In addition to soluble proteins, several membrane-bound costimulatory molecules play a fundamental role in the regulation of immune responses. These molecules include CD40, CD40 ligand, CD27, CD80, CD86 and CD 150 (SLAM), and they are typically expressed on lymphoid cells after activation via antigen recognition or through cell-cell interactions.
T helper (TH) cells, key regulators of the immune system, are capable of producing a large number of different cytokines, and based on their cytokine synthesis pattern TH cells are divided into two subsets (Paul and Seder (1994) Cell 76: 241-251). THI cells produce high levels of IL-2 and IFN- and no or minimal levels of IL-4, IL-5 and IL-13. In contrast, TH2 cells produce high levels of IL-4, IL-5 and IL-13, and IL-2 and IFN- production is minimal or absent. TH1 cells activate macrophages, dendritic cells and augment the cytolytic activity of CD8+cytotoxic T lymphocytes and NK cells (Id.), whereas TH2 cells provide efficient help for B cells and they also mediate allergic responses due to the capacity of TH2 cells to induce IgE isotype switching and differentiation of B cells into IgE secreting cell (De Vries and Punnonen (1996) In Cytokine regulation of humoral immunity: basic and clinical aspects. Eds. Snapper, C. M., John Wiley and Sons, Ltd., West Sussex, UK, p. 195-215). The exact mechanisms that regulate the differentiation of T helper cells are not fully understood, but cytokines are believed to play a major role. IL-4 has been shown to direct TH2 differentiation, whereas IL-12 induces development of TH1 cells (Paul and Seder, supra.). In addition, it has been suggested that membrane bound costimulatory molecules, such as CD80, CD86 and CD150, can direct TH1 and/or TH2 development, and the same molecules that regulate TH cell differentiation also affect activation, proliferation and differentiation of B cells into Ig-secreting plasma cells (Cocks et al. (1995) Nature 376: 260-263; Lenschow et al. (1996) Immunity 5: 285-293; Punnonen et al. (1993) Proc. Nat""l. Acad. Sci. USA 90: 3730-3734; Punnonen et al. (1997) J Exp. Med. 185: 993-1004).
Studies in both man and mice have demonstrated that the cytokine synthesis profile of T helper (TH) cells plays a crucial role in determining the outcome of several viral, bacterial and parasitic infections. High frequency of TH1 cells generally protects from lethal infections, whereas dominant TH2 phenotype often results in disseminated, chronic infections. For example, TH1 phenotype is observed in tuberculoid (resistant) form of leprosy and TH2 phenotype in lepromatous, multibacillary (susceptible) lesions (Yamamura et al. (1991) Science 254: 277-279). Similarly, late-stage HIV patients have TH2-like cytokine synthesis profiles, and TH1 phenotype has been proposed to protect from AIDS (Maggi et al. (1994) J Exp. Med. 180: 489-495). Furthermore, the survival from meningococcal septicemia is genetically determined based on the capacity of peripheral blood leukocytes to produce TNF- and IL-10. Individuals from families with high production of IL-10 have increased risk of fatal meningococcal disease, whereas members of families with high TNF- production were more likely to survive the infection (Westendorp et al. (1997) Lancet 349: 170-173).
Cytokine treatments can dramatically influence TH1/TH2 cell differentiation and macrophage activation, and thereby the outcome of infectious diseases. For example, BALB/c mice infected with Leishmania major generally develop a disseminated fatal disease with a TH2 phenotype, but when treated with anti-IL-4 mAbs or IL-12, the frequency of TH1 cells in the mice increases and they are able to counteract the pathogen invasion (Chatelain et al. (1992) J Immunol. 148: 1182-1187). Similarly, IFN- protects mice from lethal Herpes Simplex Virus (HSV) infection, and MCP-1 prevents lethal infections by Pseudomonas aeruginosa or Salmonella typhimurium. In addition, cytokine treatments, such as recombinant IL-2, have shown beneficial effects in human common variable immunodeficiency (Cunningham-Rundles et al. (1994) N. Engl. J Med. 331: 918-921).
The administration of cytokines and other molecules to modulate immune responses in a manner most appropriate for treating a particular disease can provide a significant tool for the treatment of disease. However, presently available immunomodulator treatments can have several disadvantages, such as insufficient specific activity, induction of immune responses against, the immunomodulator that is administered, and other potential problems. Thus, a need exists for immunomodulators that exhibit improved properties relative to those currently available. The present invention fulfills this and other needs.
Erythrocytes infected with the malaria parasite P. falciparum disappear from the peripheral circulation as they mature from the ring stage to trophozoites (Bignami and Bastianeli, Reforma Medica (1889) 6:1334-1335). This phenomenon, known as sequestration, results from parasitized erythrocyte (xe2x80x9cPExe2x80x9d) adherence to microvascular endothelial cells in diverse organs (Miller, Am. J Trop. Med. Hyg. (1969) 18:860-865). Sequestration is associated temporally with expression of knob protrusions (Leech et al., J. Cell. Biol. (1984) 98:1256-1264), expression of a very large antigenically variant surface protein, called PfEMPI (Aley et al., J. Exp. Med. (1984) 160:1585-1590; Leech et al., J. Exp. Med. (1984) 159:1567-1575; Howard et al., Molec. Biochem. Parasitol. (1988) 27:207-223), and expression of new receptor properties which mediate adherence to endothelial cells (Miller, supra; Udeinya et al., Science (1981) 213:555-557. Endothelial cell surface proteins such as CD36, thrombospondin (TSP) and ICAM-1 have been identified as major host receptors for mature PE. See, e.g., Barnwell et al., J. Immunol. (1985) 135:3494-3497; Roberts et al., Nature (1985) 318:64-66; and Berendt et al., Nature (1989) 341:57-59.
PE sequestration confers unique advantages for P. falciparum parasites (Howard and Gilladoga, Blood (1989) 74:2603-2618), but also contributes directly to the acute pathology of P. falciparum (Miller et al., Science (1994) 264:1878-1883). Of the four human malarias, only P. falciparum infection is associated with neurological impairment and cerebral pathology seen-increasingly in severe drug-resistant malaria (Howard and Gilladoga, supra).
Although the genesis of human cerebral malaria is likely due to a combination of factors including particular parasite phenotypes (Berendt et al., Parasitol. Today (1994) 10:412-414), inappropriate immune responses and the phenotype of endothelial cell surface molecules in the cerebral microvasculature (Pasloske and Howard, Ann. Rev. Med. (1994) :283-295), adherence of PE to cerebral blood vessels and consequent local microvascular occlusion is a major contributing factor. See, e.g., Berendt et al., supra; Patnaik et al., Am. J Trop. Med. Hyg. (1994) 51:642-647.
The capacity of P. falciparum PE to express variant forms of PFEMP1 contributes to the special virulence of this parasite. Variant parasites can evade variant-specific antibodies elicited by earlier infections. The P. falciparum variant antigens have been defined in vitro using antiserum prepared in Aotus monkeys infected with individual parasite strains (Howard et al., Molec. Biochem. Parasitol. (1988) 27:207-223). Antibodies raised against a particular parasite will only react by PE agglutination, indirect immuno-fluorescence or immunoelectronmicroscopy with PE from the same strain (van Schravendijk et al., Blood (1991) 78:226-236).
Such studies with PE from malaria patients in diverse geographic locations and sera from the same or different patients confirm that PE in natural isolates express variant surface antigens and that individual patients respond to infection by production of isolate-specific antibodies (Marsh and Howard, Science (1986) 231:150-153; Aguiar et al., Am. J. Trop. Med. Hyg. (1992) 47:621-632; Iqbal et al., Trans. R. Soc. Trop. Med. Hyg. (1993) 87:583-588. Expression of a variant antigen on PE has also been demonstrated in several simian, murine and human malaria species, including P. knowlesi (Brown and Brown, Nature (1965) 208:1286-1288; Barnwell et al., Infect. Immun. (1983) 40:985-994), P. chabaudi (Gilks et al., Parasite Immunol. (1990) 12:45-64; Brannan et al., Proc. R. Soc. Lond. Biol. Sci. (1994) 256:71-75), P. fragile (Handunnetti et al., J. Exp. Mod. (1987) 165:1269-1283) and P. vivax (Mendis et al., Am. J. Txop. Med. Hyg. (1988) 38:42-46). Laboratory studies with P. knowlesi (Brown and Brown, supra; Barnwell et al., supra) or P. falciparum (Hommel et al., J. Exp. Med. (1983) 157:1137-1148) in monkeys and P. chabaudi in mice (Gilks et al., supra) confirmed that antigenic variation at the PE surface is associated with prolonged or chronic infection and the capacity to repeatedly re-establish blood infection in previously infected animals. Studies with cloned parasites demonstrated that antigenic variants can arise with extraordinary frequency, e.g., 2% per generation with P. falciparum (Roberts et al., Nature (1992) 357:689-692) and 1.6% per generation with P. chabaudi (Brannan et al., supra).
PFEMP1 was identified as a 125I-labeled, size diverse protein (200-350 kD) on PE that is lacking from uninfected erythrocytes, and that is also labeled by biosynthetic incorporation of radiolabeled amino acids (Leech et al., J. Exp. Med. (1984) 159:1567-1575; Howard et al., Molec. Biochem. Parasitol. (1988) 27:207-223). PFEMP1 is not extracted from PE by neutral detergents such as Triton X-100 but is extracted by SDS, suggesting that it is linked to the erythrocyte cytoskeleton (Aley et al., J. Med. Exp. (1984) 160:1585-1590). After addition of excess Triton X-100, PfEMP1 is immunoreactive with appropriate serum antibodies (Howard et al., (1988), supra). Mild trypsinization of intact PE rapidly cleaves PfEMP1 from the cell surface (Leech et al., J. Exp. Mod. (1984) 159:1567-1575). PFEMP1 bears antigenically diverse epitopes since it is immunoprecipitated from particular strains of P. falciparum by antibodies from sera of Aotus monkeys infected with the same strain, but not by antibodies from animals infected with heterologous strains (Howard et al. (1988), supra). Knobless PE derived from parasite passage in splenectomized Aotus monkeys (Aley et al., supra) do not express surface PfEMPl and are not agglutinated with sera from immune individuals or infected monkeys (Howard et al. (1988), supra; Howard and Gilladoga, Blood (1989) 74:2603-2618). In general, sera that react with the PE surface by indirect immunofluorescence and antibody-mediated PE agglutination are the only sera to immunoprecipitate 125I-labeled PfEMP1 from any particular strain (Howard et al., (1988), supra; van Schravendijk et al., Blood (1991) 78:226-236; Biggs et al., J. Immunol. (1992) 149:2047-2054).
The adherence of parasitized erythrocytes to endothelial cells is mediated by multiple receptor/counter-receptor interactions, including CD36, thrombospondin and intracellular adhesion molecule-1 (ICAMxe2x80x941) as the major host cell receptors (Howard and Gilladoga, Blood (1989) 74:2603-2618, Pasloske and Howard, Ann. Rev. Med. (1994) 45:283-295).
Vascular cell adhesion molecule-1 (VCAM-1) and endothelial leukocyte adhesion molecule-1 (ELAM-1) have also been implicated as additional endothelial cell receptors that can mediate adherence of a minority of P. falciparum PE (Ockenhouse, et al., J. Exp. Med. (1992) 176:1183-1189, and Howard and Paslaske, supra). The adherence receptors on the surface of PE has not yet been conclusively identified, and several molecules, including AG 332 (Udomsangpetch, et al., Nature (1989) 338:763-765), modified band 3 (Crandall, et al., Proc. Nat""l Acad. Sci. USA (1993) 90:4703-4707), Sequestrin (Ockenhouse, Proc. Nat""l Acad. Sci. USA (1991) 88:3175-3179), and PFEMP1 (Howard and Gilladoga, supra, and Pasloske and Howard, supra), have been proposed as candidates. Several pieces of indirect evidence have linked expression of PFEMP1 with the acquisition of new host protein receptor properties on the surface of PE (Howard and Gilladoga, supra; Pasloske and Howard, Ann. Rev. Med. (1994) 45:283-295). PE adherence is correlated with the expression of PFEMP1 on the surface of mature stage PE (Leech, et al., J. Exp. Med. (1984) 159:1567-1575). Alterations in the adherence phenotype of the PE selected for in vitro are usually associated with the emergence of new forms of PFEMP1 (Biggs, et al., J. Immunol. (1992) 149:2047-2054; Roberts, et al., Nature (1992) 357:689-692). Mild trypsinization of intact mature PE cleaves the extracellular portion of PFEMP1 and at the same time, reduces or eliminates PE cytoadherence (Leech, et al., supra) Previously described antibody mediated blockade or reversal of cytoadherence is strain specific and is correlated with the ability of the reacting sera to agglutinate the corresponding PE and to immunoprecipitate the surface labeled 125I-PfEMP1 (Howard, et al., Molec. Biochem. Parasitol. (1988) 27:207-224). Pfalhesin (modified band 3) have been shown to bind CD36 under non-physiological conditions (Crandall, et al., Exp. Parasitol. (1994) 78:203-209). Sequestrin, which appears to be homologous to PfEMP 1, extracted with TX 100 from knobless PE, was shown to bind to immobilized CD36 (Ockenhouse, Proc. Nat""l Acad. Sci. USA (1991) 88:3175-3179).
The complex nature and/or mechanism of malarial antigenic variation, and its particular virulence has created a need for methods and compositions which may be useful in the treatment diagnosis and prevention of malaria infections. The present invention meets these and other needs.
The approach, termed directed evolution, of experimentally modifying a biological molecule towards a desirable property, can be achieved by mutagenizing one or more parental molecular templates and by idendifying any desirable molecules among the progeny molecules. Currently available technologies in directed evolution include methods for achieving stochastic (i.e. random) mutagenesis and methods for achieving non-stochastic (non-random) mutagenesis. However, critical shortfalls in both types of methods are identified in the instant disclosure.
In prelude, it is noteworthy that it may be argued philosophically by some that all mutagenesisxe2x80x94if considered from an objective point of viewxe2x80x94is non-stochastic; and furthermore that the entire universe is undergoing a process thatxe2x80x94if considered from an objective point of viewxe2x80x94is non-stochastic. Whether this is true is outside of the scope of the instant consideration. Accordingly, as used herein, the terms xe2x80x9crandomnessxe2x80x9d, xe2x80x9cuncertaintyxe2x80x9d, and xe2x80x9cunpredictabilityxe2x80x9d have subjective meanings, and the knowledge, particularly the predictive knowledge, of the designer of an experimental process is a determinant of whether the process is stochastic or non-stochastic.
By way of illustration, stochastic or random mutagenesis is exemplified by a situation in which a progenitor molecular template is mutated (modified or changed) to yield a set of progeny molecules having mutation(s) that are not predetermined. Thus, in an in vitro stochastic mutagenesis reaction, for example, there is not a particular predetermined product whose production is intended; rather there is an uncertaintyxe2x80x94hence randomnessxe2x80x94regarding the exact nature of the mutations achieved, and thus also regarding the products generated. In contrast, non-stochastic or non-random mutagenesis is exemplified by a situation in which a progenitor molecular template is mutated (modified or changed) to yield a progeny molecule having one or more predetermined mutations. It is appreciated that the presence of background products in some quantity is a reality in many reactions where molecular processing occurs, and the presence of these background products does not detract from the non-stochastic nature of a mutagenesis process having a predetermined product.
Thus, as used herein, stochastic mutagenesis is manifested in processes such as error-prone PCR and stochastic shuffling, where the mutation(s) achieved are random or not predetermined. In contrast, as used herein, non-stochastic mutagenesis is manifested in instantly disclosed processes such as gene site-saturation mutagenesis and synthetic ligation reassembly, where the exact chemical structure(s) of the intended product(s) are predetermined.
In brief, existing mutagenesis methods that are non-stochastic have been serviceable in generating from one to only a very small number of predetermined mutations per method application, and thus produce per method application from one to only a few progeny molecules that have predetermined molecular structures. Moreover, the types of mutations currently available by the application of these non-stochastic methods are also limited, and thus so are the types of progeny mutant molecules.
In contrast, existing methods for mutagenesis that are stochastic in nature have been serviceable for generating somewhat larger numbers of mutations per method applicationxe2x80x94though in a random fashion and usually with a large but unavoidable contingency of undesirable background products. Thus, these existing stochastic methods can produce per method application larger numbers of progeny molecules, but that have undetermined molecular structures. The types of mutations that can be achieved by application of these current stochastic methods are also limited, and thus so are the types of progeny mutant molecules.
It is instantly appreciated that there is a need for the development of non-stochastic mutagenesis methods that:
1) Can be used to generate large numbers of progeny molecules that have predetermined molecular structures;
2) Can be used to readily generate more types of mutations;
3) Can produce a correspondingly larger variety of progeny mutant molecules;
4) Produce decreased unwanted background products;
5) Can be used in a manner that is exhaustive of all possibilities; and
6) Can produce progeny molecules in a systematic and non-repetitive way.
The instant invention satisfies all of these needs.
Directed Evolution Supplements Natural Evolution: Natural evolution has been a springboard for directed or experimental evolution, serving both as a reservoir of methods to be mimicked and of molecular templates to be mutagenized. It is appreciated that, despite its intrinsic process-related limitations (in the types of favored and/or allowed mutagenesis processes) and in its speed, natural evolution has had the advantage of having been in process for millions of years and and throughout a wide diversity of environments. Accordingly, natural evolution (molecular mutagenesis and selection in nature) has resulted in the generation of a wealth of biological compounds that have shown usefulness in certain commercial applications.
However, it is instantly appreciated that many unmet commercial needs are discordant with any evolutionary pressure and/or direction that can be found in nature. Moreover, it is often the case that when commercially useful mutations would otherwise be favored at the molecular level in nature, natural evolution often overrides the positive selection of such mutations, e.g. when there is a concurrent detriment to an organism as a whole (such as when a favorable mutation is accompanied by a detrimental mutation).
Additionally, natural evolution is often slow, and favors fidelity in many types of replication. Additionally still, natural evolution often favors a path paved mainly by consecutive beneficial mutations while tending to avoid a plurality of successive negative mutations, even though such negative mutations may prove beneficial when combined, or may leadxe2x80x94through a circuitous routexe2x80x94to final state that is beneficial.
Moreover, natural evolution advances through specific steps (e.g. specific mutagenesis and selection processes), with avoidance of less favored steps. For example, many nucleic acids do not reach close enough proximity to each other in a operative environment to undergo chimerization or incorporation or other types of transfers from one species to another. Thus, e.g., when sexual intercourse between 2 particular species is avoided in nature, the chimerization of nucleic acids from these 2 species is likewise unlikely, with parasites common to the two species serving as an example of a very slow passageway for inter-molecular encounters and exchanges of DNA. For another example, the generation of a molecule causing self-toxicity or self-lethality or sexual sterility is avoided in nature. For yet another example, the propagation of a molecule having no particular immediate benefit to an organism is prone to vanish in subsequent generations of the organism. Furthermore, e.g., there is no selection pressure for improving the performance of molecule under conditions other than those to which it is exposed in its endogenous environment; e.g. a cytoplasmic molecule is not likely to acquire functional features extending beyond what is required of it in the cytoplasm. Furthermore still, the propagation of a biological molecule is susceptible to any global detrimental effectsxe2x80x94whether caused by itself or notxe2x80x94on its ecosystem. These and other characteristics greatly limit the types of mutations that can be propagated in nature.
On the other hand, directed (or experimental) evolutionxe2x80x94particularly as provided hereinxe2x80x94can be performed much more rapidly and can be directed in a more streamlined manner at evolving a predetermined molecular property that is commercially desirable where nature does not provide one and/or is not likely to provide. Moreover, the directed evolution invention provided herein can provide more wide-ranging possibilities in the types of steps that can be used in mutagenesis and selection processes. Accordingly, using templates harvested from nature, the instant directed evolution invention provides more wide-ranging possibilities in the types of progeny molecules that can be generated and in the speed at which they can be generated than often nature itself might be expected to in the same length of time.
In a particular exemplification, the instantly disclosed directed evolution methods can be applied iteratively to produce a lineage of progeny molecules (e.g. comprising successive sets of progeny molecules) that would not likely be propagated (i.e., generated and/or selected for) in nature, but that could lead to the generation of a desirable downstream mutagenesis product that is not achievable by natural evolution.
Previous Directed Evolution Methods Are Suboptimal: Mutagenesis has been attempted in the past on many occasions, but by methods that are inadequate for the purpose of this invention. For example, previously described non-stochastic methods have been serviceable in the generation of only very small sets of progeny molecules (comprised often of merely a solitary progeny molecule). By way of illustration, a chimeric gene has been made by joining 2 polynucleotide fragments using compatible sticky ends generated by restriction enzyme(s), where each fragment is derived from a separate progenitor (or parental) molecule. Another example might be the mutagenesis of a single codon position (i.e. to achieve a codon substitution, addition, or deletion) in a parental polynucleotide to generate a single progeny polynucleotide encoding for a single site-mutagenized polypeptide.
Previous non-stochastic approaches have only been serviceable in the generation of but one to a few mutations per method application. Thus, these previously described non-stochastic methods thus fail to address one of the central goals of this invention, namely the exhaustive and non-stochastic chimerization of nucleic acids. Accordingly previous non-stochastic methods leave untapped the vast majority of the possible point mutations, chimerizations, and combinations thereof, which may lead to the generation of highly desirable progeny molecules.
In contrast, stochastic methods have been used to achieve larger numbers of point mutations and/or chimerizations than non-stochastic methods; for this reason, stochastic methods have comprised the predominant approach for generating a set of progeny molecules that can be subjected to screening, and amongst which a desirable molecular species might hopefully be found. However, a major drawback of these approaches is thatxe2x80x94because of their stochastic naturexe2x80x94there is a randomness to the exact components in each set of progeny molecules that is produced. Accordingly, the experimentalist typically has little or no idea what exact progeny molecular species are represented in a particular reaction vessel prior to their generation. Thus, when a stochastic procedure is repeated (e.g. in a continuation of a search for a desirable progeny molecule), the re-generation and re-screening of previously discarded undesirable molecular species becomes a labor-intensive obstruction to progress, causing a circuitousxe2x80x94if not circularxe2x80x94path to be taken. The drawbacks of such a highly suboptimal path can be addressed by subjecting a stochastically generated set of progeny molecules to a labor-incurring process, such as sequencing, in order to identify their molecular structures, but even this is an incomplete remedy.
Moreover, current stochastic approaches are highly unsuitable for comprehensively or exhaustively generating all the molecular species within a particular grouping of mutations, for attributing functionality to specific structural groups in a template molecule (e.g. a specific single amino acid position or a sequence comprised of two or more amino acids positions), and for categorizing and comparing specific grouping of mutations. Accordingly, current stochastic approaches do not inherently enable the systematic elimination of unwanted mutagenesis results, and are, in sum, burdened by too many inherently shortcomings to be optimal for directed evolution.
In a non-limiting aspect, the instant invention addresses these problems by providing non-stochastic means for comprehensively and exhaustively generating all possible point mutations in a parental template. In another non-limiting aspect, the instant invention further provides means for exhaustively generating all possible chimerizations within a group of chimerizations. Thus, the aforementioned problems are solved by the instant invention.
Specific shortfalls in the technological landscape addressed by this invention include:
1) Site-directed mutagenesis technologies, such as sloppy or low-fidelity PCR, are ineffective for systematically achieving at each position (site) along a polypeptide sequence the full (saturated) range of possible mutations (i.e. all possible amino acid substitutions).
2) There is no relatively easy systematic means for rapidly analyzing the large amount of information that can be contained in a molecular sequence and in the potentially colossal number or progeny molecules that could be conceivably obtained by the directed evolution of one or more molecular templates.
3) There is no relatively easy systematic means for providing comprehensive empirical information relating structure to function for molecular positions.
4) There is no easy systematic means for incorporating internal controls, such as positive controls, for key steps in certain mutagenesis (e.g. chimerization) procedures. 5) There is no easy systematic means to select for a specific group of progeny molecules, such as full-length chimeras, from among smaller partial sequences.
An exceedingly large number of possibilities exist for the purposeful and random combination of amino acids within a protein to produce useful hybrid proteins and their corresponding biological molecules encoding for these hybrid proteins, i.e., DNA, RNA. Accordingly, there is a need to produce and screen a wide variety of such hybrid proteins for a desirable utility, particularly widely varying random proteins.
The complexity of an active sequence of a biological macromolecule (e.g., polynucleotides, polypeptides, and molecules that are comprised of both polynucleotide and polypeptide sequences) has been called its information content (xe2x80x9cICxe2x80x9d), which has been defined as the resistance of the active protein to amino acid sequence variation (calculated from the minimum number of invariable amino acids (bits) required to describe a family of related sequences with the same function). Proteins that are more sensitive to random mutagenesis have a high information content.
Molecular biology developments, such as molecular libraries, have allowed the identification of quite a large number of variable bases, and even provide ways to select functional sequences from random libraries. In such libraries, most residues can be varied (although typically not all at the same time) depending on compensating changes in the context. Thus, while a 100 amino acid protein can contain only 2,000 different mutations, 20100 sequence combinations are possible.
Information density is the IC per unit length of a sequence. Active sites of enzymes tend to have a high information density. By contrast, flexible linkers of information in enzymes have a low information density.
Current methods in widespread use for creating alternative proteins in a library format are error-prone polymerase chain reactions and cassette mutagenesis, in which the specific region to be optimized is replaced with a synthetically mutagenized oligonucleotide. In both cases, a substantial number of mutant sites are generated around certain sites in the original sequence.
Error-prone PCR uses low-fidelity polymerization conditions to introduce a low level of point mutations randomly over a long sequence. In a mixture of fragments of unknown sequence, error-prone PCR can be used to mutagenize the mixture. The published error-prone PCR protocols suffer from a low processivity of the polymerase. Therefore, the protocol is unable to result in the random mutagenesis of an average-sized gene. This inability limits the practical application of error-prone PCR. Some computer simulations have suggested that point mutagenesis alone may often be too gradual to allow the large-scale block changes that are required for continued and dramatic sequence evolution. Further, the published error-prone PCR protocols do not allow for amplification of DNA fragments greater than 0.5 to 1.0 kb, limiting their practical application. In addition, repeated cycles of error-prone PCR can lead to an accumulation of neutral mutations with undesired results, such as affecting a protein""s immunogenicity but not its binding affinity.
In oligonucleotide-directed mutagenesis, a short sequence is replaced with a synthetically mutagenized oligonucleotide. This approach does not generate combinations of distant mutations and is thus not combinatorial. The limited library size relative to the vast sequence length means that many rounds of selection are unavoidable for protein optimization. Mutagenesis with synthetic oligonucleotides requires sequencing of individual clones after each selection round followed by grouping them into families, arbitrarily choosing a single family, and reducing it to a consensus motif. Such motif is re-synthesized and reinserted into a single gene followed by additional selection. This step process constitutes a statistical bottleneck, is labor intensive, and is not practical for many rounds of mutagenesis.
Error-prone PCR and oligonucleotide-directed mutagenesis are thus useful for single cycles of sequence fine tuning, but rapidly become too limiting when they are applied for multiple cycles.
Another limitation of error-prone PCR is that the rate of down-mutations grows with the information content of the sequence. As the information content, library size, and mutagenesis rate increase, the balance of down-mutations to up-mutations will statistically prevent the selection of further improvements (statistical ceiling).
In cassette mutagenesis, a sequence block of a single template is typically replaced-by a (partially) randomized sequence. Therefore, the maximum information content that can be obtained is statistically limited by the number of random sequences (i.e., library size). This eliminates other sequence families which are not currently best, but which may have greater long term potential.
Also, mutagenesis with synthetic oligonucleotides requires sequencing of individual clones after each selection round. Thus, such an approach is tedious and impractical for many rounds of mutagenesis.
Thus, error-prone PCR and cassette mutagenesis are best suited, and have been widely used, for fine-tuning areas of comparatively low information content. One apparent exception is the selection of an RNA ligase ribozyme from a random library using many rounds of amplification by error-prone PCR and selection.
In nature, the evolution of most organisms occurs by natural selection and sexual reproduction. Sexual reproduction ensures mixing and combining of the genes in the offspring of the selected individuals. During meiosis, homologous chromosomes from the parents line up with one another and cross-over part way along their length, thus randomly swapping genetic material. Such swapping or shuffling of the DNA allows organisms to evolve more rapidly.
In recombination, because the inserted sequences were of proven utility in a homologous environment, the inserted sequences are likely to still have substantial information content once they are inserted into the new sequence.
Theoretically there are 2,000 different single mutants of a 100 amino acid protein. However, a protein of 100 amino acids has 20100 possible sequence combinations, a number which is too large to exhaustively explore by conventional methods. It would be advantageous to develop a system which would allow generation and screening of all of these possible combination mutations.
Some workers in the art have utilized an in vivo site specific recombination system to generate hybrids of combine light chain antibody genes with heavy chain antibody genes for expression in a phage system. However, their system relies on specific sites of recombination and is limited accordingly. Simultaneous mutagenesis of antibody CDR regions in single chain antibodies (scFv) by overlapping extension and PCR have been reported.
Others have described a method for generating a large population of multiple hybrids using random in vivo recombination. This method requires the recombination of two different libraries of plasmids, each library having a different selectable marker. The method is limited to a finite number of recombinations equal to the number of selectable markers existing, and produces a concomitant linear increase in the number of marker genes linked to the selected sequence(s).
In vivo recombination between two homologous, but truncated, insect-toxin genes on a plasmid has been reported as a method of producing a hybrid gene. The in vivo recombination of substantially mismatched DNA sequences in a host cell having defective mismatch repair enzymes, resulting in hybrid molecule formation has been reported.
The present invention provides multicomponent genetic vaccines that include at least one, and preferably two or more genetic vaccine components that confer upon the vaccine the ability to direct an immune response so as to achieve an optimal response to vaccination. For example, the genetic vaccines can include a component that provides optimal antigen release; a component that provides optimal production of cytotoxic T lymphocytes; a component that directs release of an immunomodulator; a component that directs release of a chemokine; and/or a component that facilitates binding to, or entry into, a desired target cell type. For example, a component can confer improved improves binding to, and uptake of, the genetic vaccine to target cells such as antigen-expressing cells or antigen-presenting cells.
Additional components include those that direct antigen peptides derived from uptake of an antigen into a cell to presentation on either Class I or Class II molecules. For example, one can include a component that directs antigen peptides to presentation on Class I molecules and comprises a polynucleotide that encodes a protein such as tapasin, TAP-1 and TAP-2, and/or a component that directs antigen peptides to presentation on Class II molecules and comprises a polynucleotide that encodes a protein such as an endosomal or lysosomal protease.
In a particularly preferred aspect, this invention provides a method for obtaining an immunomodulatory polynucleotide that has an optimized modulatory effect on an immune response, or encodes a polypeptide that has an optimized modulatory effect on an immune response, the method comprising: creating a library of non-stochastically generated progeny polynucleotides from a parental polynucleotide set; wherein optimization can thus be achieved using one or more of the directed evolution methods as described herein in any combination, permutation and iterative manner; whereby these directed evolution methods include the introduction of mutations by non-stochastic methods, including by xe2x80x9cgene site saturation mutagenesisxe2x80x9d as described herein; and whereby these directed evolution methods also include the introduction mutations by non-stochastic polynucleotide reassembly methods as described herein; including by synthetic ligation polynucleotide reassembly as described herein.
In another particularly preferred aspect, this invention provides a method for obtaining an immunomodulatory polynucleotide that has an optimized modulatory effect on an immune response, or encodes a polypeptide that has an optimized modulatory effect on an immune response, the method comprising:
screening a library of non-stochastically generated progeny polynucleotides to identify an optimized non-stochastically generated progeny polynucleotide that has, or encodes a polypeptide that has, a modulatory effect on an immune response; wherein the optimized non-stochastically generated polynucleotide or the polypeptide encoded by the non-stochastically generated polynucleotide exhibits an enhanced ability to modulate an immune response compared to a parental polynucleotide from which the library was created.
In another particularly preferred aspect, this invention provides a method for obtaining an immunomodulatory polynucleotide that has an optimized modulatory effect on an immune response, or encodes a polypeptide that has an optimized modulatory effect on an immune response, the method comprising: a) creating a library of non-stochastically generated progeny polynucleotides from a parental polynucleotide set; and b) screening the library to identify an optimized non-stochastically generated progeny polynucleotide that has, or encodes a polypeptide that has, a modulatory effect on an immune response induced by a genetic vaccine vector; wherein the optimized non-stochastically generated polynucleotide or the polypeptide encoded by the non-stochastically generated polynucleotide exhibits an enhanced ability to modulate an immune response compared to a parental polynucleotide from which the library was created; whereby optimization can thus be achieved using one or more of the directed evolution methods as described herein in any combination, permutation, and iterative manner; whereby these directed evolution methods include the introduction of point mutations by non-stochastic methods, including by xe2x80x9cgene site saturation mutagenesisxe2x80x9d as described herein; and whereby these directed evolution methods also include the introduction mutations by non-stochastic polynucleotide reassembly methods as described herein; including by synthetic ligation polynucleotide reassembly as described herein.
In another particularly preferred aspect, this invention provides a method for obtaining an immunomodulatory polynucleotide that has, an optimized expression in a recombinant expression host, the method comprising: creating a library of non-stochastically generated progeny polynucleotides from a parental polynucleotide set; whereby optimization can thus be achieved using one or more of the directed evolution methods as described herein in any combination, permutation and iterative manner; whereby these directed evolution methods include the introduction of mutations by non-stochastic methods, including by xe2x80x9cgene site saturation mutagenesisxe2x80x9d as described herein; and whereby these directed evolution methods also include the introduction mutations by non-stochastic polynucleotide reassembly methods as described herein; including by synthetic ligation polynucleotide reassembly as described herein.
In another particularly preferred aspect, this invention provides a method for obtaining an immunomodulatory polynucleotide that has an optimized expression in a recombinant expression host, the method comprising: screening a library of non-stochastically generated progeny polynucleotides to identify an optimized non-stochastically generated progeny polynucleotide that has an optimized expression in a recombinant expression host when compared to the expression of a parental polynucleotide from which the library was created.
In another particularly preferred aspect, this invention provides a method for obtaining an immunomodulatory polynucleotide that has an optimized-expression in a recombinant expression host, the method comprising: a) creating a library of non-stochastically generated progeny polynucleotides from a parental polynucleotide set; and b) screening a library of non-stochastically generated progeny polynucleotides to identify an optimized non-stochastically generated progeny polynucleotide that has an optimized expression in a recombinant expression host when compared to the expression of a parental polynucleotide from which the library was created; whereby optimization can thus be achieved using one or more of the directed evolution methods as described herein in any combination, permutation, and iterative manner; whereby these directed evolution methods include the introduction of point mutations by non-stochastic methods, including by xe2x80x9cgene site saturation mutagenesisxe2x80x9d as described herein; and whereby these directed evolution methods also include the introduction mutations by non-stochastic polynucleotide reassembly methods as described herein; including by synthetic ligation polynucleotide reassembly as described herein.
In one aspect, this invention provides that the ability to a vaccine, for example a genetic vaccine, or a component of a vaccine, for example a component of a genetic vaccine by optimizing its immunogenicity. Moreover, the present invention provides for the modification of other properties, including its:
Catalysed reaction(s)
Reaction type
Natural substrate(s)
Substrate spectrum
Product spectrum
Inhibitor(s)
Cofactor(s)/prostetic group(s)
Metal compounds/salts that affect it
Turnover number
Specific activity
Km value
pH optimum
pH range
Temperature optimum
Temperature range
It is also instantly appreciated that the serviceability of amolecule with an immunogenic effect can be affected by additional physical properties, which can likewise be modified by directed evolution as provided herein, such as how it is affected by subjection to:
Isolation/Preparation
Purification
Renaturating conditions (reversibility or retention of activity upon: heating and cooling, urea, salts, detergents, pH extremes)
Crystallization
pH
Temperature
Oxidation
Organic solvent(s)
Miscellaneous storage conditions
Moreover, the instant invention provides for the modification of molecule""s immunogenic properties properties such as
Exposure to biological compartments (stomach acids, in vivo degradation)
Expression (e.g.Transcription and/or Translation) level
mRNA stability
Any in vivo interactions with other cells or biologicals
In some embodiments, one or more of the genetic vaccine components is obtained by a method that involves: (1) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least first and second forms of a nucleic acid which can confer a desired property upon a genetic vaccine, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of recombinant nucleic acids; and (2) screening the library to identify at least one optimized recombinant component that exhibits an enhanced capacity to confer the desired property upon the genetic vaccine. If further optimization of the component is desired, the following additional steps can be conducted: (3) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least one optimized recombinant component with a further form of the nucleic acid, which is the same or different from the first and second forms, to produce a further library of recombinant nucleic acids; (4) screening the further library to identify at least one further optimized recombinant component that exhibits an enhanced capacity to confer the desired property upon the genetic vaccine; and (5) repeating (3) and (4), as necessary, until the further optimized recombinant component exhibits a further enhanced capacity to confer the desired property upon the genetic vaccine.
In some embodiments of the invention, the first form of the nucleic acid is a first member of a gene family and the second form of the nucleic acid comprises a second member of the gene family. Additional forms of the module nucleic acid can also be members of the gene family. As an example, the first member of the gene family can be obtained from a first species of organism and the second member of the gene family obtained from a second species of organism. If desired, the optimized recombinant genetic vaccine component obtained by the methods of the invention can be backcrossed by, for example, reassembling (and/or subjecting to one or more directed evolution methods described herein) the optimized recombinant genetic vaccine component with a molar excess of one or both of the first and second forms of the substrate nucleic acids to produce a further library of recombinant genetic vaccine components; and screening the further library to identify at least one optimized recombinant genetic vaccine component that further enhances the capability of a genetic vaccine vector that includes the component to modulate the immune response.
Additional embodiments of the invention provide methods of obtaining a genetic vaccine component that confers upon a genetic vaccine vector an enhanced ability to replicate in a host cell. These methods involve creating a library of recombinant nucleic acids by subjecting to reassembly (and/or one or more additonal directed evolution methods described herein) at least two forms of a polynucleotide that can confer episomal replication upon a vector that contains the polynucleotide; introducing into a population of host cells a library of vectors, each of which contains a member of the library of recombinant nucleic acids and a polynucleotide that encodes a cell surface antigen; propagating the population of host cells for multiple generations; and identifying cells which display the cell surface antigen on a surface of the cell, wherein cells which display the cell surface antigen are likely to harbor a vector that contains a recombinant vector module which enhances the ability of the vector to replicate episomally.
Genetic vaccine components that confer upon a vector an enhanced ability to replicate in a host cell can also be obtained by creating a library of recombinant nucleic acids by subjecting to reassembly (and/or one or more additonal directed evolution methods described herein) at least two forms of a polynucleotide derived from a human papillomavirus that can confer episomal replication upon a vector that contains the polynucleotide; introducing a library of vectors, each of which contains a member of the library of recombinant nucleic acids, into a population of host cells; propagating the host cells for a plurality of generations; and identifying cells that contain the vector.
In additional embodiments, the invention provides methods obtaining a genetic vaccine component that confers upon a vector an enhanced ability to replicate in a human host cell by creating a library of recombinant nucleic acids by subjecting to reassembly (and/or one or more additonal directed evolution methods described herein) at least two forms of a polynucleotide that can confer episomal replication upon a vector that contains the polynucleotide; introducing a library of genetic vaccine vectors, each of which comprises a member of the library of recombinant nucleic acids, into a test system that mimics a human immune response; and determining whether the genetic vaccine vector replicates or induces an immune response in the test system. A suitable test system can involve human skin cells present as a xenotransplant on skin of an immunocompromised non-human host animal, for example, or a non-human mammal that comprises a functional human immune system. Replication in these systems can be detected by determining whether the animal exhibits an immune response against the antigen.
The invention also provides methods of obtaining a genetic vaccine component that confers upon a genetic vaccine an enhanced ability to enter an antigen-presenting cell. These methods involve creating a library of recombinant nucleic acids by subjecting to reassembly (and/or one or more additonal directed evolution methods described herein) at least two forms of a polynucleotide that can confer episomal replication upon a vector that contains the polynucleotide; introducing a library of genetic vaccine vectors, each of which comprises a member of the library of recombinant nucleic acids, into a population of antigen-presenting or antigen-processing cells; and determining the percentage of cells in the population which contain the nucleic acid vector. Antigen- presenting or antigen-processing cells of interest include, for example, B cells, monocytes/macrophages, dendritic cells, Langerhans cells, keratinocytes, and muscle cells.
The present invention provides methods of obtaining a polynucleotide that has a modulatory effect on an immune response that is induced by a genetic vaccine, either directly (i.e., as an immunomodulatory polynucleotide) or indirectly (i.e., upon translation of the polynucleotide to create an immunomodulatory polypeptide. The methods of the invention involve: creating a library of experimentally generated (in vitro and/or in vivo) polynucleotides; and screening the library to identify at least one optimized experimentally generated (in vitro and/or in vivo) polynucleotide that exhibits, either by itself or through the encoded polypeptide, an enhanced ability to modulate an immune response than a form of the nucleic acid from which the library was created. Examples include, for example, CpG-rich polynucleotide sequences, polynucleotide sequences that encode a costimulator (e.g., B7-1, B7-2, CD1, CD40, CD154 (ligand for CD40), CD150 (SLAM), or a cytokine. The screening step used in these methods can include, for example, introducing genetic vaccine vectors which comprise the library of recombinant nucleic acids into a cell, and identifying cells which exhibit an increased ability to modulate an immune response of interest or increased ability to express an immunomodulatory molecule. For example, a library of recombinant cytokine-encoding nucleic acids can be screened by testing the ability of cytokines encoded by the nucleic acids to activate cells which contain a receptor for the cytokine. The receptor for the cytokine can be native to the cell, or can be expressed from a heterologous nucleic acid that encodes the cytokine receptor. For example, the optimized costimulators can be tested to identify those for which the cells or culture medium are capable of inducing a predominantly TH2 immune response, or a predominantly TH1 immune response.
In some embodiments, the polynucleotide that has a modulatory effect on an immune response is obtained by: (1) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least first and second forms of a nucleic acid that is, or encodes a molecule that is, involved in modulating an immune response, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of experimentally generated (in vitro and/or in vivo) polynucleotides; and (2) screening the library to identify at least one optimized experimentally generated (in vitro and/or in vivo) polynucleotide that exhibits, either by itself or through the encoded polypeptide, an enhanced ability to modulate an immune response than a form of the nucleic acid from which the library was created. If additional optimization is desired, the method can further involve: (3) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least one optimized experimentally generated (in vitro and/or in vivo) polynucleotide with a further form of the nucleic acid, which is the same or different from the first and second forms, to produce a further library of experimentally generated (in vitro and/or in vivo) polynucleotides; (4) screening, the further library to identify at least one further optimized experimentally generated (in vitro and/or in vivo) polynucleotide that exhibits an enhanced ability to modulate an immune response than a form of the nucleic acid from which the library was created; and (5) repeating (3) and (4), as necessary, until the further optimized experimentally generated (in vitro and/or in vivo) polynucleotide exhibits an further enhanced ability to modulate an immune response than a form of the nucleic acid from which the library was created.
In some embodiments of the invention, the library of experimentally generated (in vitro and/or in vivo) polynucleotides is screened by: expressing the experimentally generated (in vitro and/or in vivo) polynucleotides so that the encoded peptides or polypeptides are produced as fusions with a protein displayed on the surface of a replicable genetic package; contacting the replicable genetic packages with a plurality of cells that display the receptor; and identifying cells that exhibit a modulation of an immune response mediated by the receptor.
The invention also provides methods for obtaining a polynucleotide that encodes an accessory molecule that improves the transport or presentation of antigens by a cell. These methods involve creating a library of experimentally generated (in vitro and/or in vivo) polynucleotides by subjecting to reassembly (and/or one or more additonal directed evolution methods described herein) nucleic acids that encode all or part of the accessory molecule; and screening the library to identify an optimized experimentally generated (in vitro and/or in vivo) polynucleotide that encodes a recombinant accessory molecule that confers upon a cell an increased or decreased ability to transport or present an antigen on a surface of the cell compared to an accessory molecule encoded by the non-recombinant nucleic acids. In some embodiments, the screening step involves: introducing the library of experimentally generated (in vitro and/or in vivo) polynucleotides into a genetic vaccine vector that encodes an antigen to form a library of vectors; introducing the library of vectors into mammalian cells; and identifying mammalian cells that exhibit increased or decreased immunogenicity to the antigen.
In some embodiments of the invention, the cytokine that is optimized is interleukin-12 and the screening is performed by growing mammalian cells which contain the genetic vaccine vector in a culture medium, and detecting whether T cell proliferation or T cell differentiation is induced by contact with the culture medium. In another embodiment, the cytokine is interferon- and the screening is performed by expressing the recombinant vector module as a fusion protein which is displayed on the surface of a bacteriophage to form a phage display library, and identifying phage library members which are capable of inhibiting proliferation of a B cell line. Another embodiment utilizes B7-1 (CD80) or B7-2 (CD86) as the costimulator and the cell or culture medium is tested for ability to modulate an immune response.
The invention provides methods of using stochastic (e.g. polynucleotide shuffling and interrupted synthesis) and non-stochastic polynucleotide reassembly to obtain optimized recombinant vector modules that encode cytokines and other costimulators that exhibit reduced immunogenicity compared to a corresponding polypeptide encoded by a non-optimized vector module. The reduced immunogenicity can be detected by introducing a cytokine or costimulator encoded by the recombinant vector module into a mammal and determining whether an immune response is induced against the cytokine.
The invention also provides methods of obtaining optimized immunomodulatory sequences that encode a cytokine antagonist. For example, suitable cytokine agonists include a soluble cytokine receptor and a transmembrane cytokine receptor having, a defective signal sequence. Examples include sIL-10R and sIL-4R, and the like.
The present invention provides methods for obtaining a cell-specific binding molecule that is useful for increasing uptake or specificity of a genetic vaccine to a target cell. The methods involve: creating a library of experimentally generated (in vitro and/or in vivo) polynucleotides that by reassembling (and/or subjecting to one or more directed evolution methods described herein) a nucleic acid that encodes a polypeptide that comprises a nucleic acid binding domain and a nucleic acid that encodes a polypeptide that comprises a cell-specific binding domain; and screening the library to identify a experimentally generated (in vitro and/or in vivo) polynucleotide that encodes a binding molecule that can bind to a nucleic acid and to a cell-specific receptor. Target cells of particular interest include antigen-presenting and antigen-processing cells, such as muscle cells, monocytes, dendritic cells, B cells, Langerhans cells, keratinocytes, and M-cells.
In some embodiments, the methods of the invention for obtaining a cell-specific binding moiety useful for increasing uptake or specificity of a genetic vaccine to a target cell involve:
(1) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least first and second forms of a nucleic acid which comprises a polynucleotide that encodes a nucleic acid binding domain and at least first and second forms of a nucleic acid which comprises a cell-specific ligand that specifically binds to a protein on the surface of a cell of interest, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of recombinant binding moiety-encodingnucleic acids;
(2) transfecting into a population of host cells a library of vectors, each of which comprises: a) a binding site specific for the nucleic acid binding domain and b) a member of the library of recombinant binding moiety-encoding nucleic acids, wherein the recombinant binding moiety is expressed and binds to the binding site to form a vector-binding moiety complex;
(3) lysing the host cells under conditions that do not disrupt binding of the vector-binding moiety complex;
(4) contacting the vector-binding moiety complex with a target cell of interest; and
(5) identifying target cells that contain a vector and isolating the optimized recombinant cell-specific binding moiety nucleic acids from these target cells.
If further optimization is desired, the methods can further involve:
(6) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least one optimized recombinant binding moiety-encoding nucleic acid with a further form of the polynucleotide that encodes a nucleic acid binding domain and/or a further form of the polynucleotide that encodes a cell-specific ligand, which are the same or different from the first and second forms, to produce a further library of recombinant binding moiety-encoding nucleic acids;
(7) transfecting into a population of host cells a library of vectors that comprise: a) a binding site specific for the nucleic acid binding domain and 2) the recombinant binding moiety-encoding nucleic acids, wherein the recombinant binding moiety is expressed and binds to the binding site to form a vector-binding moiety complex;
(8) lysing the host cells under conditions that do not disrupt binding of the vector-binding moiety complex;
(9) contacting the vector-binding moiety complex with a target cell of interest and identifying target cells that contain the vector; and
(10) isolating the optimized recombinant binding moiety nucleic acids from the target cells which contain the vector; and
(11) repeating (6) through (10), as necessary, to obtain a further optimized cell-specific binding moiety useful for increasing uptake or specificity of a genetic vaccine vector to a target cell.
The invention also provides cell-specific recombinant binding moieties produced by expressing in a host cell an optimized recombinant binding moiety-encoding nucleic acid obtained by the methods of the invention.
In another embodiment, the invention provides genetic vaccines that include: a) an optimized recombinant binding moiety that comprises a nucleic acid binding domain and a cell-specific ligand, and b) a polynucleotide sequence that comprises a binding site, wherein the nucleic acid binding domain is capable of specifically binding to the binding site.
A further embodiment of the invention provides methods for obtaining an optimized cell-specific binding moiety useful for increasing uptake, efficacy, or specificity of a genetic vaccine for a target cell by:
(1) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least first and second forms of a nucleic acid that comprises a polynucleotide which encodes a non-toxic receptor binding moiety-of an enterotoxin or other toxin, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of recombinant nucleic acids;
(2) transfecting vectors that contain the library of nucleic acids into a population of host cells, wherein the nucleic acids are expressed to form recombinant cell-specific binding moiety polypeptides;
(3) contacting the recombinant cell-specific binding moiety polypeptides with a cell surface receptor of a target cell; and
(4) determining which recombinant cell-specific binding moiety polypeptides exhibit enhanced ability to bind to the target cell. Methods of enhancing uptake of a genetic vaccine vector by a target cell by coating the genetic vaccine vector with an optimized recombinant cell-specific binding moiety produced by these methods are also provided by the invention.
The present invention also provides methods for evolving a vaccine delivery vehicle, genetic vaccine vector, or a vector component to obtain an optimized delivery vehicle or component that has, or confers upon a vector, enhanced ability to enter a selected mammalian tissue upon administration to a mammal. These methods involve:
(1) reassembling (and/or subjecting to one or more directed evolution methods described herein) members of a pool of polynucleotides to produce a library of experimentally generated (in vitro and/or in vivo) polynucleotides;
(2) administering to a test animal a library of replicable genetic packages, each of which comprises a member of the library of experimentally generated (in vitro and/or in vivo) polynucleotides operably linked to a polynucleotide that encodes a display polypeptide, wherein the experimentally generated (in vitro and/or in vivo) polynucleotide and the display polypeptide are expressed as a fusion protein which is which is displayed on the surface of the replicable genetic package; and
(3) recovering replicable genetic packages that are present in the selected tissue of the test animal at a suitable time after administration, wherein recovered replicable genetic packages have enhanced ability to enter the selected mammalian tissue upon administration to the mammal.
If further optimization of the delivery vehicle is desired, the methods of the invention further involve:
(4) reassembling (and/or subjecting to one or more directed evolution methods described herein) a nucleic acid that comprises at least one experimentally generated (in vitro and/or in vivo) polynucleotide obtained from a replicable genetic package recovered from the selected tissue with a further pool of polynucleotides to produce a further library of experimentally generated (in vitro and/or in vivo) polynucleotides;
(5) administering to a test animal a library of replicable genetic packages, each of which comprises a member of the further library of experimentally generated (in vitro and/or in vivo) polynucleotides operably linked to a polynucleotide that encodes a display polypeptide, wherein the experimentally generated (in vitro and/or in vivo) polynucleotide and the display polypeptide are expressed as a fusion protein which is which is displayed on the surface of the replicable genetic package;
(6) recovering replicable genetic packages that are present in the selected tissue of the test animal at a suitable time after administration; and
(7) repeating (4) through (6), as necessary, to obtain a further optimized recombinant delivery vehicle that exhibits further enhanced ability to enter a selected mammalian tissue upon administration to a mammal. Methods of administration that are of particular interest include, for example, oral, topical, and inhalation. Where the administration is intravenous, mammalian tissues of interest include, for example, lymph node and spleen.
In another embodiment, the invention provides methods for evolving a vaccine delivery vehicle, genetic vaccine vector, or a vector component to obtain an optimized delivery vehicle or component to obtain an optimized delivery vehicle or vector component that has, or confers upon a vector containing the component, enhanced specificity for antigen-presenting cells by:
(1) reassembling (and/or subjecting to one or more directed evolution methods described herein) members of a pool of polynucleotides to produce a library of experimentally generated (in vitro and/or in vivo) polynucleotides;
(2) producing a library of replicable genetic packages, each of which comprises a member of the library of experimentally generated (in vitro and/or in vivo) polynucleotides operably linked to a polynucleotide that encodes a display polypeptide, wherein the experimentally generated (in vitro and/or in vivo) polynucleotide and the display polypeptide are expressed as a fusion protein which is which is displayed on the surface of the replicable genetic package;
(3) contacting the library of recombinant replicable genetic packages with a non-APC to remove replicable genetic packages that display non-APC-specific fusion polypeptides; and
(4) contacting the recombinant replicable genetic packages that did not bind to the non-APC with an APC and recovering those that bind to the APC, wherein the recovered replicable genetic packages are capable of specifically binding to APCs.
In an additional embodiment, the invention provides methods for evolving a vaccine delivery vehicle, genetic vaccine vector, or a vector component to obtain an optimized delivery vehicle or component to obtain an optimized delivery vehicle or vector component that has, or confers upon. a vector containing the component, an enhanced ability to enter a target cell by:
(1) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least first and second forms of a nucleic acid which encodes an invasin polypeptide, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of recombinant invasin nucleic acids;
(2) producing a library of recombinant bacteriophage, each of which displays on the bacteriophage surface a fusion polypeptide encoded by a chimeric gene that comprises a recombinant invasin nucleic acid operably linked to a polynucleotide that encodes a display polypeptide;
(3) contacting the library of recombinant bacteriophage with a population of target cells;
(4) removing unbound phage and phage which is bound to the surface of the target cells; and
(5) recovering phage which are present within the target cells, wherein the recovered phage are enriched for phage that have enhanced ability to enter the target cells.
In some embodiments, the optimized recombinant genetic vaccine vectors, delivery vehicles, or vector components obtained using these methods exhibit improved ability to enter an antigen presenting cell. These methods can involve washing the cells after the transfection step to remove vectors which did not enter an antigen presenting cell; culturing the cells for a predetermined time after transfection; lysing the antigen presenting cells; and isolating the optimized recombinant genetic vaccine vector from the cell lysate.
The invention also provides methods of evolving a bacteriophage-derived vaccine delivery vehicle to obtain a delivery vehicle having enhanced ability to enter a target cell. These methods involve the steps of
(1) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least first and second forms of a nucleic acid which encodes an invasin polypeptide, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of recombinant invasin nucleic acids;
(2) producing a library of recombinant bacteriophage, each of which displays on the bacteriophage surface a fusion polypeptide encoded by a chimeric gene that comprises a recombinant invasin nucleic acid operably linked to a polynucleotide that encodes a display polypeptide;
(3) contacting the library of recombinant bacteriophage with a population of target cells;
(4) removing unbound phage and phage which is bound to the surface of the target cells; and
(5) recovering phage which are present within the target cells, wherein the recovered phage are enriched for phage that have enhanced ability to enter the target cells. Again, if further optimization is desired, the methods can include the further steps of.
(6) reassembling (and/or subjecting to one or more directed evolution methods described herein) a nucleic acid which comprises at least one recombinant invasin nucleic acid obtained from a bacteriophage which is recovered from a target cell with a further pool of polynucleotides to produce a further library of recombinant invasin polynucleotides;
(7) producing a further library of recombinant bacteriophage, each of which displays on the bacteriophage surface a fusion polypeptide encoded by a chimeric gene that comprises a recombinant invasin nucleic acid operably linked to a polynucleotide that encodes a display polypeptide;
(8) contacting the library of recombinant bacteriophage with a population of target cells;
(9) removing unbound phage and phage which is bound to the surface of the target cells; and
(10) recovering phage which are present within the target cells; and
(11) repeating (6) through (10), as necessary, to obtain a further optimized recombinant delivery vehicle which exhibits further have enhanced ability to enter the target cells.
In some embodiments the methods of evolving a bacteriophage-derived vaccine delivery vehicle to obtain a delivery vehicle having enhanced ability to enter a target cell can include the additional steps of
(12) inserting into the optimized recombinant delivery vehicle a polynucleotide which encodes an antigen of interest, wherein the antigen of interest is expressed as a fusion polypeptide which comprises a second display polypeptide;
(13) administering the delivery vehicle to a test animal; and (14) determining whether the delivery vehicle is capable of inducing a CTL response in the test animal.
Alternatively, the following steps can be employed:
(12) inserting into the optimized recombinant delivery vehicle a polynucleotide which encodes an antigen of interest, wherein the antigen of interest is expressed as a fusion polypeptide which comprises a second display polypeptide;
13) administering the delivery vehicle to a test animal; and
(14) determining whether the delivery vehicle is capable of inducing neutralizing antibodies against a pathogen which comprises the antigen of interest. An example of a target cell of interest for these methods is an antigen-presenting cell.
The present invention provides recombinant multivalent antigenic polypeptides that include a first antigenic determinant from a first disease-associated polypeptide and at least a second antigenic determinant from a second disease-associated polypeptide. The disease-associated polypeptides can be selected from the group consisting of cancer antigens, antigens associated with autoimmunity disorders, antigens associated with inflammatory conditions, antigens associated with allergic reactions, antigens associated with infectious agents, and other antigens that are associated with a disease condition.
In another embodiment, the invention provides a recombinant antigen library that contains recombinant nucleic acids that encode antigenic polypeptides. The libraries are typically obtained by reassembling (and/or subjecting to one or more directed evolution methods described herein), at least first and second forms of a nucleic acid which includes a polynucleotide sequence that encodes a disease-associated antigenic polypeptide, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of recombinant nucleic acids.
Another embodiment of the invention provides methods of obtaining a polynucleotide that encodes a recombinant antigen having improved ability to induce an immune response to a disease condition. These methods involve:
(1) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least first and second forms of a nucleic acid which comprises a polynucleotide sequence that encodes an antigenic polypeptide that is associated with the disease condition, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of recombinant nucleic acids; and
(2) screening the library to identify at least one optimized recombinant nucleic acid that encodes an optimized recombinant antigenic polypeptide that has improved ability to induce an immune response to the disease condition. These methods optionally further involve:
(3) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least one optimized recombinant nucleic acid with a further form of the nucleic acid, which is the same or different from the first and second forms, to produce a further library of recombinant nucleic acids;
(4) screening the further library to identify at least one further optimized recombinant nucleic acid that encodes a polypeptide that has improved ability to induce an immune response to the disease condition; and
(5) repeating (3) and (4), as necessary, until the further optimized recombinant nucleic acid encodes a polypeptide that has improved ability to induce an immune response to the disease condition.
In some embodiments, the optimized recombinant nucleic acid encodes a multivalent antigenic polypeptide and the screening is accomplished by expressing the library of recombinant nucleic acids in a phage display expression vector such that the recombinant antigen is expressed as a fusion protein with a phage polypeptide that is displayed on a phage particle surface; contacting the phage with a first antibody that is specific for a first serotype of the pathogenic agent and selecting those phage that bind to the first antibody; and contacting those phage that bind to the first antibody with a second antibody that is specific for a second serotype of the pathogenic agent and selecting those phage that bind to the second antibody; wherein those phage that bind to the first antibody and the second antibody express a multivalent antigenic polypeptide.
In additional embodiments, the invention provides methods of obtaining a recombinant genetic vaccine component that confers upon a genetic vaccine an enhanced ability to induce a desired immune response in a mammal. These methods involve: (1) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least first and second forms of a nucleic acid which comprise a genetic vaccine vector, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of recombinant genetic vaccine vectors; (2) transfecting the library of recombinant vaccine vectors into a population of mammalian cells selected from the group consisting of peripheral blood T cells, T cell clones, freshly isolated monocytes/macrophages and dendritic cells; (3) staining the cells for the presence of one or more cytokines and identifying cells which exhibit a cytokine staining pattern indicative of the desired immune response; and (4) obtaining recombinant vaccine vector nucleic acid sequences from the cells which exhibit the desired cytokine staining pattern.
Also provided by the invention are methods of improving the ability of a genetic vaccine vector to modulate an immune response by: (1) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least first and second forms of a nucleic acid which comprise a genetic vaccine vector, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of recombinant genetic vaccine vectors; (2) transfecting the library of recombinant genetic vaccine vectors into a population of antigen presenting cells; and (3) isolating from the cells optimized recombinant genetic vaccine vectors which exhibit enhanced ability to modulate a desired immune response.
Another embodiment of the invention provides methods of obtaining a recombinant genetic vaccine vector that has an enhanced ability to induce a desired immune response in a mammal upon administration to the skin of the mammal. These methods involve: (1) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least first and second forms of a nucleic acid which comprise a genetic vaccine vector, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of recombinant genetic vaccine vectors; (2) topically applying the library of recombinant genetic vaccine vectors to skin of a mammal; (3) identifying vectors that induce an immune response; and (4) recovering genetic vaccine vectors from the skin cells which contain vectors that induce an immune response.
The invention also provides methods of inducing an immune response in a mammal by topically applying to skin of the mammal a genetic vaccine vector, wherein the genetic vaccine vector is optimized for topical application through use of stochastic (e.g. polynucletide shuffling and interrupted synthesis) and non-stochastic polynucleotide reassembly. In some embodiments, the genetic vaccine is administered as a formulation selected from the group consisting of a transdermal patch, a cream, naked DNA, a mixture of DNA and a transfection-enhancing agent. Suitable transfection-enhancing agents include one or more agents selected from the group consisting of a lipid, a liposome, a protease, and a lipase.
Alternatively, or in addition, the genetic vaccine can be administered after pretreatment of the skin by abrasion or hair removal.
In another embodiment, the invention provides methods of obtaining an optimized genetic vaccine component that confers upon a genetic vaccine containing the component an enhanced ability to induce or inhibit apoptosis of a cell into which the vaccine is introduced. These methods involve: (1) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least first and second forms of a nucleic acid which comprise a nucleic acid that encodes an apoptosis-modulating polypeptide, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of recombinant nucleic acids; (2) transfecting the library of recombinant nucleic acids into a population of mammalian cells; (3) staining the cells for the presence of a cell membrane change which is indicative of apoptosis initiation; and (4) obtaining recombinant apoptosis-modulating genetic vaccine components from the cells which exhibit the desired apoptotic membrane changes.
Other embodiments of the invention provide methods of obtaining a genetic vaccine component that confers upon a genetic vaccine reduced susceptibility to a CTL immune response in a host mammal. These methods can involve: (1) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least first and second forms of a nucleic acid which comprises a gene that encodes an inhibitor of a CTL immune response, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of recombinant CTL inhibitor nucleic acids; (2) introducing genetic vaccine vectors which comprise the library of recombinant CTL inhibitor nucleic acids into a plurality of human cells; (3) selecting cells which exhibit reduced MHC class I molecule expression; and (4) obtaining optimized recombinant CTL inhibitor nucleic acids from the selected cells. Methods of obtaining a genetic vaccine component that confers upon a genetic vaccine reduced susceptibility to a CTL immune response in a host mammal, The invention also provides methods of obtaining a genetic vaccine component that confers upon a genetic vaccine reduced susceptibility to a CTL immune response in a host mammal. These methods involve: (1) reassembling (and/or subjecting to one or more directed evolution methods described herein) at least first and second forms of a nucleic acid which comprises a gene that encodes an inhibitor of a CTL immune response, wherein the first and second forms differ from each other in two or more nucleotides, to produce a library of recombinant CTL inhibitor nucleic acids; (2) introducing viral vectors which comprise the library of recombinant CTL inhibitor nucleic acids into mammalian cells; (3) identifying mammalian cells which express a marker gene included in the viral vectors a predetermined time after introduction, wherein the identified cells are resistant to a CTL response; and (4) recovering as the genetic vaccine component the recombinant CTL inhibitor nucleic acids from the identified cells.
It is a general object of the invention to provide proteins and polypeptides that are derived from PfEMP1 proteins, nucleic acids encoding these proteins and antibodies that are specifically immunoreactive with these proteins. It is a further object to provide methods of using these various compositions in diagnosis, treatment or prevention of the onset of symptoms of a malaria parasite infection. It is a further object to provide methods of screening compounds to identify further compositions which may be used in these methods.
In one embodiment, the present invention provides substantially pure polypeptides which have amino acid sequences substantially homologous to the amino acid sequence of a PFEMP1 protein, or biologically active fragments thereof.
In preferred aspects, the polypeptides of the present invention are substantially homologous to the amino acid sequence shown, described and/or referenced herein (including incorporated by reference), biologically active fragments or analogues thereof. Also provided are pharmaceutical compositions comprising these polypeptides.
In another embodiment, the present invention provides nucleic acids which encode the above-described polypeptides. Particularly preferred nucleic acids will be substantially homologous to a part or whole of the nucleic acid sequence shown, described and/or referenced herein (including incorporated by reference) or the nucleic acid encoding for the sequences shown, described and/or referenced herein (including incorporated by reference). The present invention also provides expression vectors comprising these nucleic acid sequences and cells capable of expressing same.
In an additional embodiment, the present invention provides antibodies which recognize and bind PfEMP1 polypeptides or biologically active fragments thereof. More preferred are those peptides which recognize and bind PFEMP1 proteins associated with infection by more than one variant of P. falciparum.
In a further embodiment, the present invention provides methods of inhibiting the formation of PFEMP1/ligand complex, comprising contacting PFEMP1 or its ligands with polypeptides of the present invention.
In a related embodiment, the present invention provides methods of inhibiting sequestration of erythrocytes in a patient suffering from a malaria infection, comprising administering to said patient, an effective amount of a polypeptide of the present invention. such administration may be carried out prior to or following infection.
In still another embodiment, the present invention provides a method of detecting the presence or absence of PFEMP1 in a sample. The method comprises exposing the sample to an antibody of the invention, and detecting binding, if any, between the antibody and a component of the sample.
In an additional embodiment, the present invention provides a method of determining whether a test compound is an antagonist of PFEMP1/ligand complex formation. The method comprises incubating the test compound with PFEMP1 or a biologically active fragment thereof, and its ligand, under conditions which permit the formation of the complex. The amount of complex formed in the presence of the test compound is determined and compared with the amount of complex formed in the absence of the test compound. A decrease in the amount of complex formed in the presence of the test compound is indicative that the compound is an antagonist of PFEMP1/ligand complex formation.
This invention also relates generally to the field of nucleic acid engineering and correspondingly encoded recombinant protein engineering. More particularly, the invention relates to the directed evolution of nucleic acids and screening of clones containing the evolved nucleic acids for resultant activity(ies) of interest, such nucleic acid activity(ies) and/or specified protein, particularly enzyme, activity(ies) of interest.
Mutagenized molecules provided by this invention may have chimeric molecules and molecules with point mutations, including biological molecules that contain a carbohydrate, a lipid, a nucleic acid, and/or a protein component, and specific but non-limiting examples of these include antibiotics, antibodies, enzymes, and steroidal and non-steroidal hormones.
This invention relates generally to a method of: 1) preparing a progeny generation of molecule(s) (including a molecule that is comprised of a polynucleotide sequence, a molecule that is comprised of a polypeptide sequence, and a molecules that is comprised in part of a polynucleotide sequence and in part of a polypeptide sequence), that is mutagenized to achieve at least one point mutation, addition, deletion, and/or chimerization, from one or more ancestral or parental generation template(s); 2) screening the progeny generation molecule(s)xe2x80x94preferably using a high throughput methodxe2x80x94for at least one property of interest (such as an improvement in an enzyme activity or an increase in stability or a novel chemotherapeutic effect); 3) optionally obtaining and/or cataloguing structural and/or and functional information regarding the parental and/or progeny generation molecules; and 4) optionally repeating any of steps 1) to 3).
In a preferred embodiment, there is generated (e.g. from a parent polynucleotide template)xe2x80x94in what is termed xe2x80x9ccodon site-saturation mutagenesisxe2x80x9dxe2x80x94a progeny generation of polynucleotides, each having at least one set of up to three contiguous point mutations (i.e. different bases comprising a new codon), such that every codon (or every family of degenerate codons encoding the same amino acid) is represented at each codon position. Corresponding toxe2x80x94and encoded byxe2x80x94this progeny generation of polynucleotides, there is also generated a set of progeny polypeptides, each having at least one single amino acid point mutation. In a preferred aspect, there is generatedxe2x80x94in what is termed xe2x80x9camino acid site-saturation mutagenesisxe2x80x9d xe2x80x94one such mutant polypeptide for each of the 19 naturally encoded polypeptide-forming alpha-amino acid substitutions at each and every amino acid position along the polypeptide. This yieldxe2x80x94for each and every amino acid position along the parental polypeptidexe2x80x94a total of 20 distinct progeny polypeptides including the original amino acid, or potentially more than 21 distinct progeny polypeptides if additional amino acids are used either instead of or in addition to the 20 naturally encoded amino acids
Thus, in another aspect, this approach is also serviceable for generating mutants containingxe2x80x94in addition to and/or in combination with the 20 naturally encoded polypeptide-forming alpha-amino acidsxe2x80x94other rare and/or not naturally-encoded amino acids and amino acid derivatives. In yet another aspect, this approach is also serviceable for generating mutants by the use ofxe2x80x94in addition to and/or in combination with natural or unaltered codon recognition systems of suitable hostsxe2x80x94altered, mutagenized, and/or designer codon recognition systems (such as in a host cell with one or more altered tRNA molecules).
In yet another aspect, this invention relates to recombination and more specifically to a method for preparing polynucleotides encoding a polypeptide by a method of in vivo re-assortment of polynucleotide sequences containing regions of partial homology, assembling the polynucleotides to form at least one polynucleotide and screening the polynucleotides for the production of polypeptide(s) having a useful property.
In yet another preferred embodiment, this invention is serviceable for analyzing and cataloguingxe2x80x94with respect to any molecular property (e.g. an enzymatic activity) or combination of properties allowed by current technologyxe2x80x94the effects of any mutational change achieved (including particularly saturation mutagenesis). Thus, a comprehensive method is provided for determining the effect of changing each amino acid in a parental polypeptide into each of at least 19 possible substitutions. This allows each amino acid in a parental polypeptide to be characterized and catalogued according to its spectrum of potential effects on a measurable property of the polypeptide.
In another aspect, the method of the present invention utilizes the natural property of cells to recombine molecules and/or to mediate reductive processes that reduce the complexity of sequences and extent of repeated or consecutive sequences possessing regions of homology.
It is an object of the present invention to provide a method for generating hybrid polynucleotides encoding biologically active hybrid polypeptides with enhanced activities. In accomplishing these and other objects, there has been provided, in accordance with one aspect of the invention, a method for introducing polynucleotides into a suitable host cell and growing the host cell under conditions that produce a hybrid polynucleotide.
In another aspect of the invention, the invention provides a method for screening for biologically active hybrid polypeptides encoded by hybrid polynucleotides. The present method allows for the identification of biologically active hybrid polypeptides with enhanced biological activities.